Transducer devices employing relative changes in the acoustical propagation characteristics of surface waves traveling on opposite surfaces of a thin elastic cantilever beam yield a measure of the degree of flexing or surface strain of the elastic member. A multiplexed phase comparison loop and signal processing circuit alternately cooperates with the opposite surface waves of the transducer to supply a digital output proportional to strain and relatively free of drift, mode locking, and other spurious interactions.

A surface acoustic wave sensor system in which a predetermined level of coupling between two surface acoustic wave arrays is intentionally provided in order to couple radio frequency energy from one into the other and thereby, in cooperative effect with attendant oscillator circuits and a filter, results in the development of a difference frequency which is a function of the sensed condition.

An improved surface acoustic wave sensor in which two surface acoustic wave arrays are disposed in predetermined overlapping relationship by the use of a sealing compound which both establishes a thin sealed cavity and spaces the two surface acoustic wave arrays apart a predetermined distance, thereby eliminating the need for spacing rings or the like.

A force or fluid pressure transducer comprises two plate-like crystals. The force is applied to the first of the two crystals in a direction generally along the crystal faces by two seatings situated at opposing edges of the crystal. An oscillating portion of this first crystal changes its frequency by an amount which is a very accurate measure of the force, providing the ambient temperature of the instrument remains constant. The present invention resides in a second crystal secured to the first crystal at particular force insensitive points, there being very small spacing between the two crystals. The second crystal sustains a negligibly small amount of the force and hence a similar oscillating portion of this second crystal undergoes negligibly small frequency change. Means are provided for adjusting the steady-state temperature behavior of one crystal with respect to that of the other in order to remove residual errors. The instrument output signal is formed by generating the difference frequency between the two crystals. This difference frequency changes only negligibly when the instrument is subjected to ambient temperature changes and hence provides superior performance to earlier inventions.

Disclosed is a surface acoustic wave interferometer, including a substrate on which are disposed a first reflector and a second reflector so as to define a multimode resonant cavity therebetween. A third reflector is positioned on the substrate so that a single mode resonant cavity is defined between the second and third reflectors. An input transducer generates surface acoustic waves in the single mode cavity, while an output transducer detects the interference between surface acoustic waves in the multimode and single mode cavities. A base is rigidly affixed to the substrate in the region of the single mode cavity so that a force applied to the substrate will alter the surface acoustic wave propagation characteristics within the multimode cavity.